The Yankees’ starting pitching has gone from supposed strength to complete shambles, with Michael Pineda out for the year, Phil Hughes out of sync and Freddy Garcia out of the rotation.

Into this mess steps rookie David Phelps, replacing Garcia and making his first major league start tonight in Kansas City.

“I’m really excited. I’ll try as best I can to take it like any other game, but it is a big deal,” said Phelps, who flew ahead to Kansas City before last night’s game with Baltimore at the Stadium. “It’ll be awesome. Hopefully [I can] go out and do what I’ve been doing.

“You’ve got to go pitch-to-pitch. It’s as simple as that. You’ve got to go out and not worry about what’s going to happen, just stay in the moment and take it pitch-to-pitch. Just worry about the pitch you’re throwing. Don’t worry about the next one. Don’t worry about too far ahead. Focus on what you can, in the moment.’’

He has managed to do that through his first seven big-league relief appearances, with no decisions but a solid 3.57 ERA. Now, after the Yankee pulled the struggling Garcia from the rotation, the 25-year-old Phelps will make tonight’s start at Kauffman Stadium, just 3 1⁄2 hours from his St. Louis home.

With a bloated 5.83 ERA, the Yankee’ rotation is the second-worst in the majors. But, beyond tonight, nothing is promised to Phelps.

“I learned early on, especially here, you start thinking about the future, you’re just going to prove yourself wrong. I’m going to just worry about [tonight] and go from there,’’ said Phelps. “All I know is I’m starting [tonight]. That’s as far as it goes.

“They don’t necessarily need to [profess any faith in me]. Just this opportunity in-and-of itself expressed confidence that I can go out and give some innings. Any time you’re in position to be a starter on this team, you’re in good company. With the quality of arms we have … it’s not something to be taken lightly.’’

Phelps pitched to a 2.08 ERA this spring to edge Adam Warren and D.J. Mitchell for the long-man role. After making his big-league debut on April 8 at Tampa Bay, he stretched out to 78 pitches over 5 1⁄3 innings six days later versus Anaheim, and threw 66 pitches in a four-inning stint April 21 in Boston.

After Phelps tossed three scoreless innings against Detroit on April 28, and Garcia struggled again, Joe Girardi turned to the rookie. He said Phelps will be on a 75-90 pitch limit tonight, and admitted concern over how the rookie could respond making his starting debut in front of friends and family.

“You worry about that a bit,’’ said Girardi. “But the thing that’ll probably help him is that he’s been thrust into a role he’s never done before, and not in an easy situation, and done OK. So he’s got that nervousness part of it done.

“Managing some of the other things — first start, first time your family is going to see you — can be difficult. Hopefully he can get in his little area and focuses on what he needs to do.’’

Phelps, who estimated he’ll have 25 friends and family in the stands, added “It’s really nice being that close to home. If it’s going to be in any other ballpark other than St. Louis, that’s the closest one. So it’s good in the sense I can give back to the people who sacrificed so much for me to be where I am today — my parents, my brother, my wife, all my friends.’’